github.com/zuoyebang/bitalosdb@v1.1.1-0.20240516111551-79a8c4d8ce20/internal/base/merger.go (about)

     1  // Copyright 2021 The Bitalosdb author(hustxrb@163.com) and other contributors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package base
    16  
    17  import "io"
    18  
    19  type Merge func(key, value []byte) (ValueMerger, error)
    20  
    21  type ValueMerger interface {
    22  	MergeNewer(value []byte) error
    23  	MergeOlder(value []byte) error
    24  	Finish(includesBase bool) ([]byte, io.Closer, error)
    25  }
    26  
    27  type Merger struct {
    28  	Merge Merge
    29  	Name  string
    30  }
    31  
    32  type AppendValueMerger struct {
    33  	buf []byte
    34  }
    35  
    36  func (a *AppendValueMerger) MergeNewer(value []byte) error {
    37  	a.buf = append(a.buf, value...)
    38  	return nil
    39  }
    40  
    41  func (a *AppendValueMerger) MergeOlder(value []byte) error {
    42  	buf := make([]byte, len(a.buf)+len(value))
    43  	copy(buf, value)
    44  	copy(buf[len(value):], a.buf)
    45  	a.buf = buf
    46  	return nil
    47  }
    48  
    49  func (a *AppendValueMerger) Finish(includesBase bool) ([]byte, io.Closer, error) {
    50  	return a.buf, nil, nil
    51  }
    52  
    53  var DefaultMerger = &Merger{
    54  	Merge: func(key, value []byte) (ValueMerger, error) {
    55  		res := &AppendValueMerger{}
    56  		res.buf = append(res.buf, value...)
    57  		return res, nil
    58  	},
    59  
    60  	Name: "bitalosdb.concatenate",
    61  }